1. Field of the Invention
The present invention relates to a method for determining the amount of a tracer present in fluid from a well. The present invention particularly relates to determining the amount of tracer present in fluid from an oil and gas well.
2. Background of the Art
The present Invention relates generally to hydrocarbon (oil and gas) production from wells drilled in the earth, hereinafter referred to as “oil wells.” Drilling a hole into the earth to reach oil and gas bearing formations is expensive which limits the number of wells that can be economically drilled. It follows then that it is desirable to maximize both and the overall recovery of hydrocarbon held in the formation and the rate of flow from the subsurface formation to the surface, where it can be recovered.
One way in which to maximize production is the process known as fracturing. Hydraulic fracturing involves literally breaking or fracturing a portion of the hydrocarbon bearing formation surrounding an oil well by injecting a specialized fluid into the wellbore directed at the face of the geologic formation at pressures sufficient to initiate and/or extend a fracture in the formation. Ideally, what this process creates is not a single fracture, but a fracture zone, i.e., a zone having multiple fractures, or cracks in the formation, through which hydrocarbon can more readily flow to the wellbore.
Creating a fracture in a hydrocarbon-bearing formation requires several materials. Often these materials, if not removed from the oil well, can interfere with oil and gas production. Even the drilling mud used to lubricate a drill bit during the drilling of an oil well can interfere with oil and gas production. Taking too long to remove such materials can increase the cost to the operator of the well by delaying production and causing excess removal expenses. Not being thorough in removing such materials can increase the cost to the operator of the well through lower production rates and possible lost production.
Measures taken to remove unwanted or unneeded materials are usually inexact. Sometimes additional fluids are used to flush out unwanted materials in the well bore. In other situations, reservoir fluids flow can make estimating return flow very difficult, particularly if the reservoir fluids are incompatible with the injected materials.
In other instances, particularly in situations where oil wells produce fluids from more than a single point in the well, it can be desirable to determine where fluids are entering an oil well. For example, when a well is piercing more than one reservoir, and one of the reservoirs begins to produce too little hydrocarbon, it may be desirable to plug that portion of the well to avoid excess water production.
It would be desirable in the art of oil production to be able to determine how much of a given material is left in an oil well after a drilling, fracturing or any other operation requiring the injection of materials into an oil well. In applications where fluid is being produced from more than a single location in an oil well, it would be desirable to be able determine what fluids are being produced at each production point in the well. It would be particularly desirable if such a determination could be made using an inexpensive and environmentally benign method. If would also be desirable if such a determination could be made quickly, on site, and cost efficiently.